Organophilic clays (hereinafter referred to as "organoclays") find wide application as rheological additives in organic based systems. One such system of particular interest for the present invention is based upon an unsaturated polyester. It may be noted in this regard that fumed silica is currently widely used as a direct additive for rheological control of unsaturated polyester resin systems. Organoclays, typically representing the reaction product of a smectite-type clay with a quaternary ammonium compound, have also been used for these purposes, but normally require a pregel of the organoclay in styrene for proper viscosity development prior to addition to the resin system. This is discussed in numerous prior art patents, e.g. in U.S. Pat. Nos. 4,473,675 and 4,240,951.
Various producers of organoclays have had limited success preparing direct add organoclays which do not require a pregel with an unsaturated polyester resin/styrene system, see for example U.S. Pat. No. 4,753,974. By and large, however, these prior efforts have not produced a product which is broadly competitive with fumed silica.
Another field pertinent to the present invention where the thixotropic properties of organoclays are of importance is drilling fluids. In the course of drilling an oil, gas or water well by means of rotary drilling tools, the drill pipe and bit are rotated to drill out the borehole. A so-called "drilling fluid" or "drilling mud" is circulated downwardly through the hollow drill stem and bit to the bottom of the borehole and then upwardly through the surface through the annular space between the drill stem and the interior of the borehole. This drilling fluid comprises a suspension of solid material in a liquid medium and may contain other added agents. The drilling fluid lubricates and cools the drill bit, and suspends and carries cuttings out of the borehole. In order to perform these and other functions the drilling fluid should desirably have certain physical characteristics. These include a viscosity that enables it to be pumped and circulated. Also the fluid should have sufficient gel strength that cuttings will remain suspended in the borehole if circulation of the fluid is stopped, as for example by a mechanical failure.
In those instances where the drilling fluid has an oil base, organoclays have long been used as thickeners and/or suspending agents. These organoclays, representing the reaction product of a smectite-type clay with a quaternary ammonium compound, are well-known in the art and are disclosed in numerous U.S. patents such as U.S. Pat. Nos. 4,105,578, 4,569,923 and 4,664,842. The drilling fluids of the prior art which incorporate these organoclays have provided satisfactory performance under relatively moderate operating temperatures. However where drilling temperatures begin to exceed around 300.degree. F. conventional organoclays other than those based on hectorite begin to perform poorly. Particularly in the higher range extending to 450-550.degree. F. or higher, these conventional drilling fluids (including those based on hectorite organoclays) have displayed an undesirable loss in viscosity and gel strength.
In addition to their functions as thixotropes, organoclays find numerous other applications. Recently, e.g. processes have been disclosed which are useful in producing composite materials composed of a organic polymer and a smectite-type clay mineral, with the mineral being connected to the polymer through ionic bonding. For example, in Kawasumi et al., U.S. Pat. No. 4,810,734 a process is disclosed wherein a smectite-type clay mineral is contacted with a swelling agent in the presence of a dispersion medium thereby forming a complex. The complex containing the dispersion medium is mixed with a monomer, and the monomer is then polymerized. The patent states that the swelling agent acts to expand the interlayer distance of the clay mineral, thereby permitting the clay mineral to take monomers into the interlayer space. The swelling agent is a compound having a onium ion and a functional ion capable of reacting and bonding with a polymer compound. Among the polymers utilizable are polyamide resins, vinyl polymers, thermosetting resins, polyester resins, polyamide resins and the like. Related disclosures are found in U.S. Pat. Nos. 4,739,007 and 4,889,885.
The swelling agents used in the Karasumi et al. and related patents cited above, technically qualify as organoclays. In general, organoclays represent the reaction product of a smectite-type clay with a higher alkyl containing ammonium compound (often a quaternary), and have long been known for use in gelling of organic liquids such as lubricating oils, linseed oil, toluene and the like and for use as rheological additives in a variety of organic based liquid systems and solvents. The general procedures and chemical reactions pursuant to which these organoclays are prepared are well known. Thus under appropriate conditions the organic compound which contains a cation will react by ion exchange with clays which contain a negative layer lattice and exchangeable cations to form the organoclay products. If the organic cation contains at least one alkyl group containing at least ten carbon atoms then the resultant organoclays will have the property of swelling in certain organic liquids. Among the further prior art patents which discuss at length aspects of the preparation and properties of organoclays are U.S. Pat. Nos. 2,531,427, 2,966,506, 3,974,125, 3,537,994, and 4,081,496.
As utilized in the present specification, the term "smectite" or "smectite-type clays" refers to the general class of clay minerals with expanding crystal lattices, with the exception of vermiculite. This includes the dioctahedral smectites which consist of montmorillonite, beidellite, and nontronite, and to the trioctahedral smectites, which includes saponite, hectorite, and sauconite. Also encompassed are smectite-clays prepared synthetically, e.g. by hydrothermal processes as disclosed in U.S. Pat. Nos. 3,252,757; 3,586,468; 3,666,407; 3,671,190; 3,844,978; 3,844,979; 3,852,405; and 3,855,147.
The phase dispersions exhibited by the composite materials thus far discussed are relatively coarse, and differ materially in this respect from nanocomposites. The latter are a relatively new class of materials which exhibit ultrafine phase dimensions, typically in the range 1-100 nm. Experimental work on these materials has generally shown that virtually all types and classes of nanocomposites lead to new and improved properties when compared to their micro- and macrocomposite counterparts. The number of nanocomposites based on smectite-type clays and linear thermoplastics is growing. Wang and Pinnavaia, e.g., have recently reported delamination of an organically modified smectite in an epoxy resin by heating an onium ion exchanged form of montmorillonite with epoxy resin to temperatures of 200-300.degree. C. Chemistry of Materials, vol. 6, pages 468-474 (April, 1994). Moreover in U.S. Pat. No. 5,554,670 an epoxy-silicate nanocomposite is disclosed which is prepared by dispersing an organically modified smectite-type clay in an epoxy resin together with diglycidyl ether of bisphenol-A (DGEBA), and curing in the presence of either nadic methyl anhydride (NMA), and/or benzyldimethyl amine (BDMA), and/or boron trifluoride monoethylamine (BTFA) at 100-200.degree. C. Molecular dispersion of the layered silicate within the crosslinked epoxy matrix is obtained, with smectite layer spacings of 100 .ANG. or more and good wetting of the silicate surface by the epoxy matrix. Additional recent references evidencing the increasing interest in nanocomposites incorporating organoclays in polymer matrices include U.S. Pat. Nos. 5,164,440; 5,385,776; 5,552,469; and 5,578,672;